You can find the files required to graft stock animations on your own characters about half way down the page on the link below...
http://www.thegamecreators.com/?m=view_product&id=2001&page=Files
There is no problem selling characters in the store that use the stock animations as long as the characters themselves are all your own work.
EDIT : If you copy the FPE file from an existing stock character and change the bits that relate to your asset, such as texture and model, etc. This will then ensure that all the animation and limb data is setup correctly. The gun the character wields can then be set in the FPE file itself.
This is also a good way to learn. Rather than trying to write everything from nothing and becoming frustrated when it fails to do what it should, by taking something that is already known to work and tweaking/improving it until it breaks you can find out where things are going wrong.
TGC Store Artist Tag : Kasseyus